Stardock announces that Sins of a Solar Empire: Rebellion is smashing all the company's previous sales records. They offer some details on this, including some praise for the impact of sales on Steam, clearly putting the rivalry over once having owned the competing Impulse service in the rearview:

The company has sold more than 100,000 copies digitally to date of Rebellion

The company’s internal projections factored in a large “cannibalization” percentage of its own direct sales through its web site and sales from its former digital distribution platform Impulse (now owned and operated by GameStop.)

Sale stats showed that Steam sales did NOT cannibalize those sales

Steam sales instead replaced what Stardock has usually seen via sell-in at retail